http://www.nps.gov/policy/section512.pdf
Protecting the Right of Individuals To Bear arms in Units of the National Park System and the National Wildlife Refuge System - The Secretary of the Interior shall not promulgate or enforce any regulation that prohibits an individual from possessing a firearm including an assembled or functional firearm in any unit of the National Park System or the National Wildlife Refuge System if --
(1) the individual is not otherwise prohibited by law from possessing the firearm; and
(2) the possession of the firearm is in compliance with the law of the State in which the unit of the National Park System or the National Wildlife Refuge System is located.